Electron device and the like adapted for alternating current



July9, 1929. REMYERS y 1,719,988

' i ELEGTRQN DEVICE AND '1;HE LIKE ADAPTED FOR ALTERNATING CURRENT Filed Jan. 26, 1.923

FIG- 1 INVENTOR IPH/.PH E MYERS ATTORNEY Patented July 9, 1929.

UNITED STATES PATENT oFFIcE.

RALPH EMERSON MYERS, OF EAST ORANGE, NEW JERSEY, ASSIGNOR T0 WESTING- HOUSE LAMP COMPANY, A CORPORATION 0F PENNSYLVANIA.

nLEGrBoN DEVICE AND THE LIKE narran non ALTERNATING CURRENT.

Application nled January 96,:1923. Serial No. 615,024.

This invention relates to electron tuloes and more'particularly to composite filamentary material for suchy devices adapted to be heated to electron-emitting temperatures by alternating current.

An object of my invention is the manufacture of electron devices and the like adapted to be operated from alternating current sources whereby storage batteries or the like, for such purpose, may be dispensed wit e Another object of my invention is the manufacture of electron-emitting lamentary material adapted to serve as hot cathodes for electron tubes and the like and be ysupplied with the necessary heat from a source of alternating current.

A further `object of my invention is the manufacture of composite electron-emitting filamentary material, in which the heating circuit for the same, when serving as a hot cathode in an electron tube or the like, is adapted to be insulated from the active electron-emitting surface thereof, whereby such electron-emitting surface is not affected by the potential 'fluctuations of the heating circuit. i'

A still further object of my invention is the manufacture of electron tubes and the like containing composite hot-cathodes, in ilamentary form, composed of a metal core adapted to be heated directly or through y,proper transformers, from a convenient source of electricity, for example, a commercial alternating-current lighting circuit, said core being encased in an insulating sheath of magnesia, thoria or other refractory insulating material carrying a good electron-emitter or surrounded by a metal sheath of a suitable conductin material, such as nickel or the like, coatedg with good electron-emission material such as the oxides of barium, strontium and the like.

Other objects and advantages of the invention will b e `clearly disclosed by the following detailed description.

In radio receiving sets and the like, it has been customary to heat the electron-emitting cathode of the radio tube or tubes by means of a storage battery or other source of direct current. The use of alternating current for heating such electron-emitting cathode has not been found feasible in the past because the rapid. fluctuations in potential and current has been found to cause a hum in the `ductive carrier be inert wit telephones. The use of direct current for heating the electron-emitting filament is not very convenient because it requires power at a voltage which is not generally available except from storage or dry batteries. Even if a commercial lighting circuit is available to furnish direct current, -it is at a voltage which is not suitable for heating the electron-emitting lilament and, asis well known, direct current is not adapted to be readily transformed to other voltages.

Alternating current, on the other hand, may be readily stepped down, by means of a suitable transformer, to such potential as is adapted for heating the electron emitter or hot cathode of a radiotron or the like. According to my invention, I have devised a composite electron-emitting filament in which the core thereof serves to heat the same `toelectron-emitting temperatures and said core is insulated from the outer electron-emitting surface, thereby adapting the core to be heated from a convenient source of alternating current without affecting the otential of the electron-emitting surface, be cause it is insulated therefrom. The core is preferably formed of a metal, such as tungsten, or an alloy, such as nickel chromium alloy, and is surrounded by refractory insulating material, such as thoria, magnesia or the like. Outside of the insulating sheath may be directly attached an active electronemission material, if such material is conductive, such as metallic thorium. If it is Idesired to use substantially non-conductive electron-emission material such as the oxides of barium and strontium, it is preferable to apply a 'conductive shleathfof platinum, nickel or the like, for example, upon which such electron-emitting oxides are deposited. In this instance, it is necessar that the conrespect to the electron-emitting material applied thereto, i. e., if a metal is used to carry, for example, a mixture of the oxides of barium and strontium, it is essential that substantially no reaction shall take` lace between said metal and said oxides w en the filament containing the same is heated.

My invention will better be understood by referring to the accompanying drawing, lin

which, v

Fig. 1 illustrates, diagrammatlcally, l radio receiving set embodying my invention; Fig. 2 is an enlarged cross-sectional view of my composite electron-emitting material after drawing to the desired size, taken, for

' example, on the line IIJ-II of Fig. 1; and,

Fig. 3 is an enlarged longitudinal crosssection of the electron-emitting cathode.

The antenna or aerial 3 (Fig. 1) may be connected through inductancc 4 and variable condenser 5, to the ground 6. A variable inductance 7 iscoupled with inductance 4 and connected to variable condenser 8, as shown. One side of the condenser 8 is connected to the electron-*emitting coating 9 of the hot cathode 11 in vevacuated electrontube or radiotron 12, and the other side of said condenser is'connected to grid 13. The innercore 14 of hot cathode 11 is insulated from the electron-emitting coating 9 by refractory insulating material 15. Inner core 14, provided with suitable leads through the bulb or tube, as shown, may be energized so thatthe hot cathode is raised to an electron-emitting temperature, by being connected to the secondary 16 of adjustable step-down 'transformer 17.

Primary 18 of said transformer 17 may be cpnnected to any suitable source of alternat-v ing current, such, for example, as a single phase alternating-current generator 19 or to a commercial alternating-current lightingcircuit through a switch 21. The plate 22` of radiotron 12 is connected to the electronemitting surface of cathode 11, through telephone receivers 24, battery 23 and switch 25.

The parts of the radio receiving circuit just described are of a simplel form to illustrate the application of my invention and it will be obvious that my invention may be used with a transmitting circuit or with any radio circuit involving the use of electron tubes.

The radio energy received by the antenna 3 is transmitted by inductance to the lgrid and varies the potential difference between the electron-emitting filament or cathode 11 and grid 13, thereby regulating the electron discharge between the hot cathode 11 and ythe plate 22 so that the proper signals are receivedin the phones 24. The step-down transformer 17 may -be adjusted to heat the core 14v of the hot cathode 11 to the desired temperature so that the requisite electron ow occurs between said cathode 11 and the plate 22. y

4,The construction of the hot cathode 11 is clearly shown in Figs. 2 and 3 which illustrate cross and longitudinal sections thereof. Said ycathode is preferablyE in lamentary form and may comprise a core of a metal of the tungsten class or', if electron-emitting oxides are employed, some other comparativelyv refractory metallic material, such as nickel chromium alloy, may be used. Such a core is encased in suitable refractory in-` sulating material 15, such as magnesia, alumma, thoria or the like. Upon this insulating material 15 may be coated or deposited an electron-emission material 9, if such material is conductive, i. e., if it is composed of thorium for example. However, if it is desired to use non-conductive electron-emission material, such as a mixture of the oxides of barium and strontium, for example, it will be necessary to apply a sheath of conductive material26 outsideof the insulating coating 15. The conductive material 26 may be any metal that is fairly refractory, such as platinum or nickel, which does not react with the superficial electron-emission material to be coated thereon.

Another embodiment of my invention may comprise a coating of thorium on an outer conductive coating of graphite, molybdenum, tungsten or the like. Thorium may be deposited in any desired manner, for example, as described and claimed in the application of Marden, Conley and Thomas, Serial No. 578,813, iiled July 31, 1922, now Patent No. 1,487,174 of March 18, 1924, electrolytic deposition of thorium, and assigned in Fig. 2, the relative proportions of the parts being about as ere Yindicated, although the exactproportions are not essential, the main idea being to form a composite body which may be swaged and drawn to ilamentary form of reasonably small cross-section without rupturin either the core 14, the sheath 26, or impairing the insulation 15 therebetween.

When the operation of swaging and drawing the composite rod to the desired size of wire has been performed, the same may be coated with suitable electron-emission'material, as, for example, passing said wire or filament, if provided with a nickel, platinum or platinum-iridium surface, through a suspension of the oxides of barium and strontium and baking lthe same thereon. If thorium is used as the electron-emission vmaterial, molybdenum, tungsten, or other similar lrefractory material should be used for the core and sheath. However, if electron-emitting oxides, such as those mentioned, are employed, nickel chromium alloy, nickel, platisealed into an electron tube 12, such as shown in Fig. 1, and leads be provided for directly heating the core 14.. It is only necessary to through the tubev 12, besides those usually provided, for connection with the electronemitting coating 9 of the filament 11.

As shown in Fig. 3, the electron-emitting cathode 11 is preferably formed by doubling a section of composite filament, such as heretofore described, so that the portions of the doubled or looped cathode lie close together, side-by-side. By thisl construction, the electrostatic and electromagnetic effects of the alternating current in the cathode loop, are minimize l .AlthoughV only one loop or doubled section is illustrated as composing'the cathode 11, I contemplate making the cathode as one or any desired number of loops, so that the resistance thereof corresponds to the impressed voltage.' If enough loops are employed, it is obvious that the resistance of the cathode can be increased to such an extent that it willbe unnecessary to use a stepdown transformer, but merely a regulating resistance, to control the source of power,

- which may be a 11() volt lighting circuit.

Even when using a transformer,l it may be found convenient to employ a regulating resistance or rheostat, (not shown) to accurately control the cathode temperature, as is usual. y v

Some of the desirable 4embodiments, of my invention, with respect to thefformation of the cathode, as illustrated in Figs. 2 and 3, are as follows. l If the electron-emitter 9 is alkaline-cart material for example, a mixture ofthe oxides of barium 4and strontium, the core 14 may consist of a metallic material such as nickel chromium alloy,.nickel, platinum or platinum-iridium. The insulation 15 may consist of thoria, magnesia or alumina. ,The sheath 26 should be formed of nickel, platinum or some other conductive inaterialnot reacting with the electron-emitting oxide or oxides used. Molybdenumandl tungsten have been found to be unsuitable for the purpose. t

On the other hand, if thorium is used as the electron-emitter, the core should consist of molybdenum, tungsten, or someother refractory metal. The insulation lmay consist of magnesia, thoria or alumina as in the previous instance. The materials preferred for the sheath 26 when thorium is used are molybdenum, tungsten, tantalum or the like, which may carry the thorium al loyed therewith or applied thereupon in any suitable manner, for example, ,by electroplating according to the application of provide one additional lead Marden, Conley and Thomas before mentioned.

Although I have described what I now considerto be the preferred embodimentsof my invention, it is to be understood that` .2. Filamentary material adapted for hot electron-emitting gcathodes. comprising a core of molybdenum surrounded by mag'n nesia msulation upon which is applied a barium and strontium. t

3. A cathode capable of being heated by alternating current for electron-emitting purposes comprising an' inner refractory metal wire, a metal sheath therearound insulated.. from the inner Wire byV refractory oxide .and coated with electron-emitting.

oxides, the component parts of-V said cathode being disposed in non-mductive relation.

4. An electron tube having an electron emitting cathode capable of being heated by alternating current'sealed therein and compri'sing an inner heating element in an outer platiniim sheath' coated with the oxides of metallic sheath, coated with alkaline earth oxides, separated from the heating element by refractory insulating material; said coreV having its op osit'e end portions disposed in closely space relation whereby to neutralize the inductive effect of the alternating heating current.

5. An electron tube having a hot cathode` sealed therein in the form of a loop having the leg portions thereof disposed. close to each other, said cathode consisting of a molybdenum core surrounded by a platinum sheath with ma esia' insulation therebetween, said plat1num`sheath being coated with a mixture df the oxides of barium and strontium. f

V6. The method Vof manufacturing composit material for .electron-emission purposes comprising inserting. aconductive core 1nto a conductlvesheath, filling the space therebetweenlwith insulating material,

drawing the same to filamentary coating said sheath with electron-emission material. fi y a In testimony whereof, I have hereunto subscribed my name this 25th day of J anuj ary, 1923. .I

RALPH EMERSON MYERS. 

